\documentclass[10pt,letterpaper]{letter}
\usepackage[latin1]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\address{your name and address} 
\signature{your signature} 
\begin{document} 
\begin{letter}{name and address of the recipient} 
\opening{saying hello} 
 
Voy a escribir otra cosa
 
\closing{saying goodbye} 
%\cc{Cclist} 
%\ps{adding a postscript} 
%\encl{list of enclosed material} 
\end{letter} 
\end{document}